1. Field of the Invention
This invention relates generally to surgical guidewires having flexible tips and methods for manufacturing such guidewires.
2. Discussion of the Prior Art
Surgical guidewires are used primarily to facilitate the placement of catheters and endoscopic instruments within the torturous paths of body conduits. For example, if it is desirable to place a catheter within the vascular system of a patient, a guidewire is first inserted into the vessel and guided through the torturous path desired for the catheter. Then the catheter is threaded over the guidewire. As the catheter is advanced, it tends to follow the direction of the guidewire so that it ultimately negotiates the same torturous path. Once the catheter is in its final operative position, the guidewire can be removed leaving the catheter to perform its desired surgical function.
Since the catheter must be constructed to facilitate its own purpose it is often too large and inflexible to be guided along the torturous path without the use of a guidewire. It follows that a major requirement for the guidewire is its ability to negotiate the torturous path. This typically requires a very flexible tip, as well as a highly torquable axial profile.
In the past, guidewires have been formed with solid cores which extend along substantially the entire length of the guidewire from its proximal end to its distal end. In order to increase the flexibility at the distal end of the guidewire, the core has been tapered and springs have been formed to begin and end on the tapered surface. Such guidewires have also been provided with coatings which closely follow the surface of the core and spring subassembly.
This construction has provided guidewires with distal tips having increased flexibility. However, certain elements of the structure have in fact added to the rigidity of the distal tips. For example, in the past, the core has extended along the entire length of the guidewire so that even in the region where flexibility is desired, the core has tended to add stiffness. The close proximity of the sheath to the core and spring have also added rigidity to this distal section. Since the coating has generally followed the supporting surface, it has provided the guidewire with a generally uneven outer configuration in the area of the spring. Where an uneven configuration might provide reduced friction forces when sliding against a hard surface, it has tended to increase friction forces with respect to soft tissue.
Solid cores in the area of the distal tip have also presented a problem when the guidewire has been severely bent. In a typical construction wherein the core extends throughout the length of the guidewire, a severe bend has forced the core to yield making it impossible for the distal tip to recover to its original configuration. Although elaborate materials, such as Nitinol have aided in this recoverability, their costs have been prohibitive for most applications.
The construction of guidewires has been relatively expensive due primarily to the elaborate methods required to form the guidewires out of complex materials using elaborate machinery for coextrusion. Of course it is always desirable to reduce manufacturing complexity and cost in order to provide products which can perform enhanced functions at a reduced cost.